Sodium zirconium carbonate and zirconium basic carbonate and methods of making the same

ABSTRACT

A method of making sodium zirconium carbonate is described which involves forming a mixture of zirconium oxychloride with soda ash and then heating at a sufficient temperature and for a sufficient time to form the sodium zirconium carbonate. Subsequent washing and filtration steps can further form parts of this process. A novel sodium zirconium carbonate is further described which contains from about 2 wt % to about 5 wt % Na + ; from about 44 wt % to about 50 wt % ZrO 2 ; from about 12 wt % to about 18 wt % CO 3   2− ; and from about 32 wt % to about 35 wt % H 2 O.

BACKGROUND OF THE INVENTION

The present invention relates to sodium zirconium carbonate, zirconiumphosphate, and zirconium basic carbonate and methods of making thesecompounds.

Sodium Zirconium Carbonate (SZC) is an amorphorous zirconium polymericcompound with the structural formula as shown:

The granular form of the material can be obtained by the following twomethods:

Method A: Reaction of granular zirconium basic sulfate with a saturatedsoda ash solution followed by washing the product to remove the sulfate.

Method B: Controlled polymeric particle growth reaction of a metastablesodium zirconium carbonate solution formed by mixing a soluble zirconiumsalt solution with an excessive amount of soda ash solution.

One industrial application of granular SZC is the conversion of thematerial to zirconium basic carbonate (ZBC) which is a commercial rawmaterial in making other zirconium chemical products. The conversion canbe made by titrating the granular SZC to pH 3.5-4.0 with an acid toremove the excessive sodium carbonate. The granular SZC used for makingZBC is usually produced by Method A. Another important application ofSZC is the conversion of the material to the granular zirconium chemicalion exchangers, namely, zirconium phosphate (ZrP) and hydrous zirconiumoxide (HZO). These zirconium ion exchange material are used commerciallyfor renal dialysis application. The quality and economic criteria, whichdictate the method of their manufacture, constitute the art of makingthe REDY® sorbent cartridge for hemodialysate regeneration currentlyused by SORB™ Technology, Inc., Oklahoma City, Okla. A recent study onthe design of a sorbent cartridge at SORB™ Technology, Inc. forperitoneal dialysis (PD) fluid regeneration indicates that the granularSZC by itself has unique properties which make it more beneficial thanHZO in contributing to the potency of the sorbent PD cartridge. Theseproperties of the material which make the cartridge adaptable to the PDtreatment conditions may be summarized as follows:

1. The material has sufficient phosphate adsorption capacity to removephosphate from the patient fluid for the treatment of hyperphosphatemiain renal disease patients.

2. The material supplements bicarbonate to the PD fluid, which can beessential to correct metabolic acidosis in patients.

3. The material prevents the pH of PD fluid from falling, which maycause depletion of bicarbonate from the patient. This allowsregenerative PD to be feasible.

In order to manufacture the granular SZC for sorbent PD applications,both quality and economic factors have to be considered. Method A cannotbe used because the product has high sulfate content that degrades thequality of the material as a sorbent. Method B has been used inproduction through the use of acid zirconium sulfate tetrahydrate (AZST)as the zirconium raw material. The process efficiency is less and themanufacture cost is higher for this process, but the ZrP made fromgranular SZC has higher ammonium adsorption capacity than that made fromzirconium basic sulfate (ZBS).

While these processes are useful, there is a need to provide a betterquality sodium zirconium carbonate and zirconium basic carbonate withuses especially in the dialysis area and further there is a need toreduce the cost of manufacturing these components.

SUMMARY OF THE PRESENT INVENTION

The feature of the present invention is to provide an improved sodiumzirconium carbonate.

A further feature of the present invention is to provide improvedmethods to make the sodium zirconium carbonate.

An additional feature of the present invention is to provide a method tomake zirconium basic carbonate.

Also, a feature of the present invention is to provide methods to makethe zirconium basic carbonate.

Another feature of the present invention is to provide an improvedzirconium phosphate and methods to make zirconium phosphates.

An additional feature of the present invention is to provide methods tomake the sodium zirconium carbonate, zirconium phosphate, and zirconiumbasic carbonate more economically and to provide methods which result ina better quality product.

Additional features and advantages of the present invention will be setforth in part in the description which follows, and in part will beapparent from the description, or may be learned by practice of thepresent invention. The objectives and other advantages of the presentinvention will be realized and obtained by means of the elements andcombinations particularly pointed out in the written description andappended claims.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein, thepresent invention relates to a method of making sodium zirconiumcarbonate which involves heating zirconium oxychloride with soda ash ata sufficient temperature and for a sufficient time to form the sodiumzirconium carbonate. Preferably, the soda ash is in the form of anaqueous slurry or solution and the zirconium oxychloride is in the formof a powder or solution. Prior to the heating, the zirconium oxychlorideand soda ash are preferably agitated or mixed by other means to form asolution mixture at ambient temperatures, such as room temperature.After the heating step, the sodium zirconium carbonate can be washed toremove impurities and any chloride.

The sodium zirconium carbonate, after the initial preparation can besubjected to a titration. Preferably, an alkaline slurry contains thesodium zirconium carbonate and the titration occurs with at least oneacidic agent, such as an acid, to obtain a pH below about 7.0. Otheradditional steps can be used in this process, such as filtering steps,washing steps, and drying steps.

The present invention further relates to a sodium zirconium carbonatewhich contains from about 2 weight percent to about 5 weight percentNa⁺;

from about 44 weight percent to about 50 weight percent ZrO₂;

from about 12 weight percent to about 18 weight percent CO₃ ²⁻; and

from about 32 weight percent to about 35 weight percent H₂O, based onthe weight of the sodium zirconium carbonate.

The present invention, in addition, relates to a method of makingzirconium basic carbonate which involves titrating an aqueous slurry ofa sodium zirconium carbonate to a pH of from about 3.5 to about 4 withan acidic agent. The sodium zirconium carbonate used to form the slurryhas a preferred moisture content of from about 15% to about 25% LOD.After titrating, the aqueous slurry is washed with water. The zirconiumbasic carbonate can then be recovered as a wet powder from the slurry byvarious techniques.

In addition, the present invention relates to a zirconium basiccarbonate characterized by a Na⁺ content of less than about 1000 ppm;

a ZrO₂ wt % of from about 35 wt % to about 40 wt %; and

a CO₃ ²⁻ of from about 8 wt % to about 10 wt % wherein the weight % isbased on the composition of the solid powder (final product). Unlessstated otherwise, all % and wt %, throughout this application, are wt %based on the weight of the final product.

The present invention further relates to a method of making zirconiumphosphate which involves heating zirconium oxychloride with soda ash ata sufficient temperature and for a sufficient time to form sodiumzirconium carbonate and treating the sodium zirconium carbonate withcaustic soda to form an alkaline hydrous zirconium oxide. Afterwards,the alkaline hydrous zirconium oxide is heated as a slurry, and anacidic agent(s) such as phosphoric acid, is added. After heating, theslurry can be cooled and an acid zirconium phosphate can be filtered offand washed to reduce unreacted leachable phosphate levels. An aqueousslurry can then be formed with the acid zirconium phosphate and thisslurry can be titrated with a basic agent, such as caustic soda, until adesired pH is reached, such as a pH of from about 5 to about 6.Afterwards, the titrated product, which is titrated zirconium phosphate,can be filtered and washed to preferably reduce the leachable sodiumions. Then, the zirconium phosphate can be dried to form a free flowingpowder preferably having a moisture level of from about 12 to about 18%LOD.

The present invention further relates to a novel zirconium phosphatewhich preferably has a Na⁺ content of from about 4 to about 6 wt %; aZrO₂ wt % of from about 34 wt % to about 37 wt %; a PO₄ ⁻% of from about41 wt % to about 43 wt %; and a H₂O wt % of from about 14 wt % to about18 wt %, based on the weight of the zirconium phosphate. The zirconiumphosphate of the present invention preferably has a good adsorptioncapacity for ammonia, Ca²⁺, Mg²⁺, and toxic heavy metals. Preferably,the zirconium phosphate has no residual sulfate or chloride andsatisfies other characteristics desirable in dialysis applications orother ion exchange applications.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are intended to provide a further explanation of the presentinvention, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this application, illustrate embodiments of the presentinvention and together with the description, serve to explain theprinciples of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing showing one embodiment of preparing sodiumzirconium carbonate.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to methods of making sodium zirconiumcarbonate and to methods of making zirconium basic carbonate andzirconium phosphate. In each instance, the starting materials arepreferably zirconium oxychloride. The present invention further relatesto novel forms of sodium zirconium carbonate, zirconium phosphate, andzirconium basic carbonate. The sodium zirconium carbonate, the zirconiumbasic carbonate, and the zirconium phosphate can be used in a variety ofindustrial applications as raw materials and further can be used inrenal dialysis applications and in other separation applications.

In more detail, in an embodiment of the present invention, the presentinvention relates to a method of making sodium zirconium carbonate. Themethod involves heating zirconium oxychloride with soda ash at asufficient temperature and for a sufficient time to form the sodiumzirconium carbonate. Prior to heating, the sodium zirconium carbonatemay be partially or completely formed.

Preferably, the soda ash is in the form of an aqueous slurry orsolution. The amount of the soda ash used to form the solution or slurryis preferably an amount to form a saturated solution or slurrycontaining soda ash. For instance, from about 260 g to about 920 g ofsoda ash per liter of water can be used to form the saturated solutionor slurry.

The zirconium oxychloride preferably has the formula ZrOCl₂.8H₂O and iscommercially available from such sources as Teledyne Wah Chang Co.,Dastech Int'l, Inc., and Zirconia Sales, Inc. Preferably, the zirconiumoxychloride and the soda ash are present in a weight ratio of from about3.0:1 to about 4.0:1; and more preferably a weight ratio of from about3.5:1 to about 4.0:1; and even more preferably a weight ratio of about3.6:1.

The zirconium oxychloride is preferably in the form of a powder orsolution. If in a solution, the zirconium oxychloride is preferablypresent in an amount of about 400 g per liter of water.

With respect to the above process, preferably, prior to the heatingstep, the zirconium oxychloride and soda ash are agitated or mixed byother means to form a solution mixture preferably at ambienttemperature, such as room temperature (e.g., from about 40° F. to about110° F.). With regard to the metastable sodium zirconium carbonatesolution which is achieved prior to the heating step, preferably, agelatinous precipitate of zirconium carbonate is formed when zirconiumoxychloride (solution or solid) is added to soda ash solution. Due tothe amphoteric property of the material, the zirconium carbonatere-dissolves in excessive soda ash solution to preferably form ametastable sodium zirconium carbonate (alkaline) solution at roomtemperature. When the mixing ratio of ZrOCl₂.8H₂O to soda ash isoptimized and the mixing temperature is preferably maintained in therange of from about 90° to about 95° F. (by the heat of reactiongenerated during mixing), the material is preferably completelydissolved to form a clear solution. Upon storage at room temperature fora few hours, the solution becomes turbid as precipitate starts to form.The turbidity of the starting solution does not affect the particle sizeand % recovery of the product. Nevertheless, it is preferred to startheating up the metastable SZC solution at once after it is formed. Inthe heating step, precipitation of SZC preferably starts to occur atabout 150° F. due to saturation. As heating is continued, polymeric SZCparticles start to grow to 30-50 micron particle size range at the finaltemperature (boiling point) of the sodium zirconium carbonate.Preferably, a sufficient temperature is the boiling temperature of themixture of the zirconium oxychloride and soda ash. For example, thetemperature of the heating can be from about 150° F. to about 250° F.(super heating under pressure) for a time of about 2 hours. Theequilibration time at the final temperature is about 2 hours. Maximumtemperature of heating and long heating time affect the resultingparticle size. When heating sodium zirconium carbonate and the soda ash,preferably the heating rate of the mixture is from about 0.5° F. toabout 1° F./minute until boiling of the mixture is achieved. The mixturecan be heated until the superheating temperature of the mixture isobtained under pressure.

Preferably, the agitation or other mixing means used to obtain themixture leads to a clear metastable solution at room temperature. Duringthe heating step, preferably, the mixture is slowly agitated or mixed byother means to obtain improved particle growth.

In the above process, and after the heating step, the sodium zirconiumcarbonate solution can be reduced in temperature from the boilingtemperature to about 150° F. or lower. This product solution containingthe sodium zirconium carbonate can be filtered off to recover the sodiumzirconium carbonate which is preferably in a granular form. Waterseparation can be achieved by any standard filtering technique, such asusing centrifuging or filtration. Afterwards, the filtered sodiumzirconium carbonate can be washed with water, such as RO water, toremove any chlorides or other impurities from the sodium zirconiumcarbonate. Typically, many of these impurities originated from the sodaash.

As a preferred part of the process, an alkaline slurry containing thesodium zirconium carbonate can then be titrated, as an option, with atleast one acidic agent to obtain a pH of below about 7 and morepreferably a pH of from about 3.5 to about 6.0 and, even more preferablya pH of about 6.0. The acidic agent used for the titration can be anyagent capable of reducing the pH of the alkaline slurry and morepreferably is an acid and, even more preferably is HCl, such as 1 N HCl.After the titration, the sodium zirconium carbonate can be filtered offas before and optionally washed with, for instance, RO water. Thiswashing step preferably reduces the amount of leachable Na⁺.

The sodium zirconium carbonate (SZC) recovered from the above-describedprocess with or without the optional steps, but preferably with theoptional steps, is generally in the form of a washed sodium zirconiumcarbonate filter cake. This sodium zirconium carbonate is thenpreferably dried and is generally dried for a sufficient time to form afree-flowing powder. The drying can occur by any technique, such asputting the filter cake on a tray and drying in an oven. Preferably, thedrying temperature is at a temperature range of from about 100° F. toabout 150° F. Other temperatures can be used. During the drying of thesodium zirconium carbonate, the moisture content that is eventuallyachieved is preferably from about 10% LOD to about 60% LOD and morepreferably from about 30% LOD to about 35% LOD. FIG. 1 sets forth apreferred process of making the SZC.

The recovered sodium zirconium carbonate preferably has an averageparticle size of from about 30 microns to about 50 microns, and otherparticle size ranges can be achieved.

The sodium zirconium carbonate of the present invention preferably, inits final form, has from about 2 wt % to about 5 wt % Na⁺;

from about 44 wt % to about 50 wt % ZrO₂;

from about 12 wt % to about 18 wt % CO₃ ²⁻; and

from about 32 wt % to about 35 wt % H₂O, based on the weight of thesodium zirconium carbonate.

The sodium zirconium carbonate of the present invention furtherpreferably satisfies the standards set forth in ANSI/AAMI RD-5-1992 onextractable toxic impurities.

Preferably, the sodium zirconium carbonate of the present inventionfurther achieves one or more of the following properties orcharacteristics:

a phosphate adsorption having a minimum capacity of from about 30 toabout 35 mg PO₄ ⁻P/gm SZC;

a minimum HCO₃ ⁻ content of from about 2 to about 4 mEq HCO₃ ⁻/gm SCZ:

a maximum leachable Na⁺ content of from about 1.5 to about 2.0 mEqNa⁺/gm SCZ;

and/or a pH range of the titrated sodium zirconium carbonate of fromabout 6 to about 7.

Preferably, the sodium zirconium carbonate of the present invention hasat least one of the above characteristics and more preferably at leasttwo or three, and even more preferably, all of the abovecharacteristics.

The sodium zirconium carbonate preferably provides the necessary potencyrequirements for peritoneal dialysis applications by providing asufficient phosphate adsorption capacity for economic use as a clinicalsorbent for the treatment of, for instance, hyperphosphatemia or renaldisease patients. Further, the sodium zirconium carbonate of the presentinvention provides the specified bicarbonate content in a peritonealdialysis fluid during applications. The present invention further hasthe minimum leachable Na+ as described above.

In the manufacture of granular SZC, the particle size of the product and% recovery can be important for the process performance especiallyeconomics, process efficiency (washing, filtration) and product quality.Bigger particle size may increase the stability of the polymericparticles against attrition loss during washing and improve thefiltration efficiency. The stability of the particles during the crystalgrowth reaction is preferably controlled by the ZrO₂% of the metastableSZC solution, the ratio of soda ash to ZrO₂ in solution, the heatingrate of the reaction, the maximum heating temperature, and the heatingtime. A recovery of 92-98% product in the particle size range 30-40microns can be achieved by adjusting the process parameters as follows:

TABLE 1 ZrO₂ % of SZC metastable solution 5.5-7.0% Reactant ratio ofsoda ash to ZrO₂ in solution 3.6:1 by weight Heating rate of particlegrowth reaction 0.5° F.-1° F./min Maximum heating temperature Boiling tosuperheating (under pressure) Continuous heating time at maximum 2 hourstemperature

The SZC titrated to different pH in the range 3-8 have variant qualitiessummarized by Table 2. Cartridge performance tests indicate that SZC pH7-8 may induce phosphate leakage and a spike of Na+ and pH in theinitial cartridge effluent when the material is tested in a cartridgefor PD application.

TABLE 2 Variant Qualities of Granular SZC for Dialysis Application as aFunction of pH Leachable SZC pH Phosphate Adsorption Na⁺ Content HCO₃ ⁻Content 3.5 35.12 mg PO₄—P/gm — — 5.0 — 0.87 mEq/gm  2.1 mEq/gm 6.0 33.9 mg PO₄—P/gm 1.88 mEq/gm 3.05 mEq/gm 8.0  33.5 mg PO₄—P/gm — —

While low pH is favorable for phosphate adsorption and reduction ofleachable Na+, it also reduces the bicarbonate content and buffercapacity of the material used for the cartridge. Thus the pH 6.0-6.5should be the optimum range, as verified by the cartridge performancetest. After titration, the material should be washed with plenty of ROwater until the Total Dissolved Solid is below 300 ppm level in order tocontrol the leachable Na⁺ content.

The filter cake after titration and washing should be tray-dried at mildtemperature (e.g., 100° F.-150° F.) to the preferred moisture level offrom about 30 to about 35% LOD. The final product is preferably notover-dried to prevent the loss of bicarbonate. Drying to differentmoisture levels can also affect the phosphate adsorption capacity of thematerial as shown in Table 3. Finally, the dried product should bestored in sealed containers to avoid loss of moisture and bicarbonatecontent.

TABLE 3 Variation of Phosphate Adsorption Capacity as a Function ofMoisture Level for Granular SZC pH 6.0 Moisture Level PhosphateAdsorption Capacity (% LOD) mg PO₄—P/gm SZC 10.6% 21.44 14.9% 22.2421.0% 24.0  28.3% 27.36 36.7% 28.8  42.9% 30.16 51.6% 29.12 57.9% 28.72

Cartridge performance tests indicate that granular SZC titrated to pH6.0 and dried to the moisture level 30-35% LOD has sufficient phosphateadsorption capacity to completely remove the uremic toxin from PD fluidfor an 8-hour treatment. The material also has sufficient bicarbonateprovision to maintain the pH of the fluid throughout dialysis. The levelof spikes of Na⁺ and pH in the initial cartridge effluent is alsotolerable and can be diminished by priming before dialysis.

In addition, the present invention also relates to a method of makingzirconium basic carbonate which preferably has the formula:

In making the zirconium basic carbonate, an aqueous slurry of sodiumzirconium carbonate is titrated to a pH of from about 3.5 to about 4.0with an acidic agent, such as an acid(s). The sodium zirconium carbonateprior to being introduced into an aqueous slurry preferably has amoisture content of from about 15% to about 25% LOD and more preferablyfrom about 15% to about 20% LOD in solid form. While any sodiumzirconium carbonate can be used, preferably the sodium zirconiumcarbonate formed from the above-described processes is used.

After titration, the aqueous slurry is preferably washed with, forinstance, RO water. Afterwards, the zirconium basic carbonate can berecovered as a wet powder from the slurry. The recovery of the zirconiumbasic carbonate can be achieved by any recovery techniques, such asvacuum filtered or centrifuging or other means. The acidic agent usedfor titration can be any agent capable of reducing the pH as describedabove but is more preferably a dilute HCl or HNO₃ or other acid ormixtures thereof. Preferably, the final washing of the zirconium basiccarbonate is to remove any sodium before any final recovery of thezirconium basic carbonate.

Also, as part of the present invention, the present invention relates toa novel zirconium basic carbonate having Na⁺ content of less than about1000 ppm;

a ZrO₂ wt % of from about 35% to about 40%; and

a CO₃ ²⁻ wt % of from about 8% to about 10%, based on the weight of thezirconium basic carbonate.

Preferably, the zirconium basic carbonate has essentially no SO₄ ²⁻ andessentially no Cl⁻ in the zirconium basic carbonate, e.g., less thanabout 0.01 wt %.

Again, the zirconium basic carbonate can be used in a variety ofindustrial applications as well as in sorbent applications.

With respect to the process of making the zirconium phosphate, theprocess involves similar steps to those used to make the sodiumzirconium carbonate. The sodium zirconium carbonate discussed above andachieved after the initial heating step and optional filtering andwashing of the sodium zirconium carbonate can be used in this process toform the zirconium phosphate of the present invention. Alternatively,other zirconium oxychlorides can be processed in the manner discussedabove to obtain the sodium zirconium carbonate which can then be usedthrough the subsequent steps described below to achieve the desiredzirconium phosphate.

In making the zirconium phosphate of the present invention, sodiumzirconium carbonate is preferably formed by heating zirconiumoxychloride with soda ash at a sufficient temperature and for asufficient time to form the sodium zirconium carbonate. The startingmaterials and the temperatures and times that are preferred can be thesame as described above with respect to making the sodium zirconiumcarbonate. The sodium zirconium carbonate formed can then be preferablycooled for instance to a temperature of about 150° F. and optionallysubjected to a filtering and washing. Afterwards, the sodium zirconiumcarbonate can then be treated with a caustic soda or other suitableagent to form alkaline hydrous zirconium oxide. This hydrous zirconiumoxide can be in the form of a slurry which is then heated, for instance,in a reactor, at a sufficient temperature and for a sufficient time withan acidic agent, such as phosphoric acid, and more preferably a dilutedtechnical grade phosphoric acid at a 1:1 ratio, with the alkalinehydrous zirconium oxide. Preferably, the heating temperature, as statedabove, is at about 180° F. to about 185° F. for about 1 hour.Afterwards, the product can be cooled to a temperature of preferablyabout 150° F. and filtered off as acid zirconium phosphate (H⁺ZrP). Theacid zirconium phosphate is preferably washed with RO water one or moretimes to reduce unreacted leachable phosphate levels. Afterwards, anaqueous slurry can be formed with the acid zirconium phosphate and thisslurry can be titrated to a pH of about 5 to about 6, and morepreferably from about 5.5 to about 6. Preferably, the titrating agent isa 50% caustic soda. Afterwards, the nitrated zirconium phosphate can befiltered and washed to reduce leachable Na⁺ and more preferably washedwith RO water to achieve a 300 ppm or less total dissolved solids tominimize leachable Na⁺.

Afterwards, the washed zirconium phosphate can be dried to achieve afree flowing powder which preferably has a moisture level of from about12 to about 18% LOD. Preferably, the drying occurs at a temperature offrom about 100° C. to about 120° C. though other temperatures can beused as long as the integrity of the powder is maintained. Preferably,the particle size of the powder is from about 30 microns to about 50microns, though other sizes can be obtained based on desired parameters.

The washing, filtering, and drying steps mentioned above can be achievedby conventional techniques known to those skilled in the art.

The zirconium phosphate preferably achieved by the process of thepresent invention has the following characteristics:

Na⁺ content from about 4 to about 6 wt %

ZrO₂ content of from about 34 to about 37 wt %;

PO₄ ⁻ content of from about 41 to about 43 wt %; and

H₂O content from about 14 to about 18 wt %, based on the weight of thezirconium phosphate.

Furthermore, the zirconium phosphate of the present invention preferablyhas an adsorption capacity for ammonia, Ca²⁺, Mg²⁺, and toxic heavymetals. More preferably, the adsorption capacity is approximately fromabout 30 mg NH₄ ⁻N/gm ZrP to about 35 mg NH₄ ⁻N/gm ZrP, and morepreferably about 30 mg NH₄ ⁻N/gm ZrP; from about 3 mEq Ca²⁺/gm ZrP toabout 5 mEq Ca²⁺/gm ZrP, and more preferably about 3 mEq Ca²⁺/gm ZrP;from about 2 mEq Mg²⁺/gm ZrP to about 3 mEq Mg²⁺/gm ZrP, and morepreferably about 2 mEq Mg²⁺/gm ZrP; and from about 5 mEq HM/gm ZrP toabout 7 mEq HM/gm ZrP, and more preferably about 6 mEq HM/gm ZrP forheavy metals (HM).

Further, the zirconium phosphate preferably has a Na⁺ content of fromabout 2 mEq Na⁺/gm ZrP to about 3 mEq Na⁺/gm ZrP, and more preferablyabout 2.4 mEq Na⁺/gm and a pH of from about 5.5 to about 6.

Also, the zirconium phosphate of the present invention preferably has aminimum leachable PO₄ ³⁻ for the material and more preferably is lessthan about 0.05 mg % PO₄ ³⁻/gm ZrP.

In addition, the zirconium phosphate preferably has an average grainsize of from about 30 to about 40 microns and has no residual sulphateor chloride (e.g., less than 0.01%). Furthermore the zirconium phosphatepreferably satisfies the ANSI/AAMI RD-5-1992 standard on extractabletoxic impurities and has a pH when in water of from about 6 to about 7.As stated earlier, the zirconium phosphate can be used in a variety ofseparation devices, such as dialysis separations.

The present invention will be further clarified by the followingexamples, which are intended to be purely exemplary of the presentinvention.

EXAMPLES Example 1

789 gm soda ash was dissolved in 3 liters deionized water. Withagitation, 610 gm ZrOCl2 powder was discharged into the soda ashsolution. Agitation was continued until the solid was completelydissolved to form a metastable solution. The metastable solution wasslowly heated up at the rate 6-10° F. per 10 minutes until the boilingor superheating temperature (under pressure) was reached. The heatingwas continued at the equilibration temperature for 1.5-2 hours. SZCparticles started to form at about 150° F. and continued to grow to30-50 microns in particle size during the equilibration. Slow agitationwas used to obtain better particle growth. The product slurry was thencooled to about 120° F. after heating. The granular SZC was filtered offand the filter cake was washed with deionized water to remove the sodiumchloride and excess carbonate. The yield of SZC wet cake was 862 gm andthe ZrO2% recovery from the metastable solution was found to be 95%.

The SZC wet cake was transferred back to 500 ml deionized water in abeaker. With agitation, the slurry was titrated with 3 N HCl.Equilibration at this pH was continued for 30 minutes and the pH wasreadjusted to 6.0 afterwards. The titrated SZC was then filtered off andwashed with deionized water until the Total Dissolved Solid in thefiltrate was less than 300 ppm. The washed filter cake was then dried atmild temperature (about 150° F.) with a tray dryer to about 30% moisturelevel to form a free-flowing powder.

Example 2 Synthesis of ZrP From Zirconium Oxychloride

The washed filter cake of SZC obtained in Example 1 was transferred to500 ml of 10% NaOH with agitation. The alkali treatment was continuedfor half an hour. Then the material was filtered and washed briefly withdeionized water. The filter cake was transferred to 1 liter of deionizedwater in the reactor. The slurry was heated up to about 185° F. 1200 gmof 1:1 diluted phosphoric acid (600 gm 76% H₃PO₄ mixed with equal volumeof water) was slowly added to the heated slurry until the addition wascomplete. Heating was then continued at 190°-195° F. for 1 hour. Theproduct slurry was then cooled to 150° F., filtered, and washed withdeionized water to remove excessive phosphate. The acid ZrP thusobtained was then titrated to pH 5.75 in 500 ml deionized water with 50%NaOH. The titrated ZrP was then filtered and rinsed with deionized waterto remove leachable Na⁺ until the Total Dissolved Solid in filtrate wasless than 300 ppm. The filter cake of titrated ZrP after washing wasthen dried to 14-18% moisture level with tray dryer to form afree-flowing power.

Other embodiments of the present invention will be apparent to thoseskilled in the art from consideration of the specification and practiceof the invention disclosed herein. It is intended that the specificationand examples be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims andequivalents thereof.

What is claimed is:
 1. A method of making a sodium zirconium carbonatefree of OH groups comprising heating a mixture of zirconium oxychlorideand soda ash at a sufficient temperature and for a sufficient time toform said sodium zirconium carbonate free of OH groups.
 2. The method ofclaim 1, further comprising, prior to said heating, agitating thezirconium oxychloride and soda ash to form a solution mixture at ambienttemperature.
 3. The method of claim 1, wherein said soda ash is in theform of an aqueous slurry or solution.
 4. The method of claim 1, whereinsaid zirconium oxychloride and soda ash are present in a weight ratio offrom about 3.0:1 to about 4.0:1.
 5. The method of claim 4, wherein saidweight ratio is from about 3.5:1 to about 4.0:1.
 6. The method of claim4, wherein said weight ratio is about 3.6:1.
 7. The method of claim 1,wherein said zirconium oxychloride is in the form of a powder orsolution.
 8. The method of claim 1, wherein said sufficient temperatureis the boiling temperature of the mixture of zirconium oxychloride andsoda ash.
 9. The method of claim 8, wherein the heating occurs for about2 hours.
 10. The method of claim 1, wherein said temperature is fromabout 150° F. to about 250° F.
 11. The method of claim 1, furthercomprising, after said heating, filtering off the sodium zirconiumcarbonate.
 12. The method of claim 11, further comprising, afterfiltering, washing any chloride or any impurities from said sodiumzirconium carbonate.
 13. The method of claim 1, further comprising,after heating, titrating an alkaline slurry comprising said sodiumzirconium carbonate with at least one acidic agent to obtain a pH ofless than about 7.0.
 14. The method of claim 13, wherein said pH is fromabout 3.5 to about 6.0.
 15. The method of claim 13, wherein said pH isabout
 6. 16. The method of claim 13, further comprising, aftertitrating, filtering off said sodium zirconium carbonate and washingsaid sodium zirconium carbonate.
 17. The method of claim 16, furthercomprising, after washing, drying said sodium zirconium carbonate. 18.The method of claim 17, wherein said drying occurs for a sufficient timeto form a free flowing powder.
 19. The method of claim 17, wherein aftersaid drying, said sodium zirconium carbonate has a moisture content offrom about 10% LOD to about 60% LOD.
 20. The method of claim 19, whereinsaid moisture content is from about 30% LOD to about 35% LOD.
 21. Themethod of claim 18, wherein said sodium zirconium carbonate has anaverage particle size of from about 30 microns to about 50 microns. 22.The method of claim 1, wherein said heating occurs at a heating rate offrom about 0.5° F. to about 1° F./minute until boiling temperature ofsaid mixture.
 23. A method of making sodium zirconium carbonatecomprising mixing zirconium oxychloride with soda ash and agitating toform a solution mixture at ambient temperatures; heating said mixture ofzirconium oxychloride and soda ash at a sufficient temperature and for asufficient time to form said sodium zirconium carbonate, wherein saidsufficient temperature is the boiling temperature of the mixture ofzirconium oxychloride and soda ash; after said heating, filtering offthe sodium zirconium carbonate; after filtering, washing any chloride orany impurities from said sodium zirconium carbonate; titrating analkaline slurry comprising said sodium zirconium carbonate with at leastone acidic agent to obtain a pH of less than about 7.0; after titrating,filtering off said sodium zirconium carbonate and washing said sodiumzirconium carbonate; and after washing, drying said sodium zirconiumcarbonate.
 24. A sodium zirconium carbonate comprising from about 2 wt %to about 5 wt % Na⁺; from about 44 wt % to about 50 wt % ZrO₂; fromabout 12 wt % to about 18 wt % CO₃ ²⁻; and from about 32 wt % to about35 wt % H₂O, based on the weight of the sodium zirconium carbonate. 25.The sodium zirconium carbonate of claim 24, wherein said sodiumzirconium carbonate satisfies ANSI/AAMI RD-5-1992 standard onextractable toxic impurities.
 26. The sodium zirconium carbonate ofclaim 24, wherein said sodium zirconium carbonate satisfies at least oneof the following characteristics: a phosphate adsorption having aminimum capacity of from about 30 to about 35 mg/PO₄-P/gm SCZ; a minimumHCO₃ ⁻ content of from about 2 to about 4 mEq HCO₃ ⁻ gm SCZ; a leachableNa⁺ content of from about 1.5 to about 2.0 mEq Na⁺/gm SCZ; or a pH rangeof titrated sodium zirconium carbonate of from about 6 to about
 7. 27.The method of claim 1, wherein said zirconium oxychloride and soda ashare mixed at a temperature of from about 40° F. to about 110° F.
 28. Themethod of claim 1, wherein said sodium zirconium carbonate has a formulaNaZrO₂CO₃.nH₂O.
 29. A method of making a sodium zirconium carbonatecomprising: heating a mixture of zirconium oxychloride and soda ash at asufficient temperature and for a sufficient time to form said sodiumzirconium carbonate; and titrating an alkaline slurry comprising saidsodium zirconium carbonate with at least one acidic agent to obtain a pHof less than about 7.0.
 30. A method of making a sodium zirconiumcarbonate comprising: heating a mixture of zirconium oxychloride andsoda ash at a sufficient temperature and for a sufficient time to formsaid sodium zirconium carbonate, wherein said heating occurs at aheating rate of from about 0.5° F. to about 1° F./minute until boilingtemperature of said mixture.